With the advent of flexible displays in military and commercial applications, there are a variety of needs for dyes that act as filters for special wavelengths such as laser light passing through the flexible display materials and screens. Recently numerous glass and flexible display manufacturers have been exploring application of these dyes in new technologies.
Ultraviolet, visible and near infrared optical absorbers or dyes currently are being used as filter materials to block or absorb specific wavelength ranges. For example, optical absorbers are used in security applications, to block specific light-emitting diodes (“LEDs”) in ATM machines, and in laser welding. Currently, these dyes work well in conditions where there is limited exposure to sunlight and moderate temperatures. Several dyes are used in LCD filter technology, but are limited to indoor use, as long as there are only moderate thermal changes and minimal to no sunlight exposure.
Although organic dyes can be utilized in absorption of specific wavelengths of light, the dyes need to maintain their optical integrity during processing conditions. To ensure high structural integrity over a variety of environmental conditions, polymers with thermal and impact resistance usually are essential. Typically these polymers result in high temperature processing conditions above 150° C., through a melt extrusion process. Melt extrusion ensures complete mixing of the dye and polymer through thermal and mechanical cycling. This process adds excess stress over a long period of time, usually beyond the heat capacity of most organic dyes.
Several chemical manufacturers such as Crysta-Lyn Chemical Company (Binghamton, N.Y.) currently make designer dyes that can be tuned to specific wavelengths, which in combination can be used to block specific ranges of light through a film. However, the dyes typically lose optical stability when heated above 100° C. Degradation during processing can cause obstruction of view or optical failure through an inability to block the specified light.
Current approaches for stabilizing dyes utilize porphyrin rings, which have a complex synthesis and lead to high cost. Another approach is to utilize metal ions such as antimony; however, these tend to be expensive and hazardous to human health and the environment.
Thus, there is a need to improve the thermal stability of optical absorbers for use in various optical and optoelectronic applications where exposure of the optical absorber to heat and/or sunlight is expected.